Control of leak zone under blade platform

ABSTRACT

A system for controlling a leakage zone under platforms of blades of a turbomachine blade-wheel by liners having edges that flare radially inwards, and that are disposed in inter-blade cavities defined by the platforms, by upstream and downstream radial walls of the blades and by the periphery of the wheel disk. One of the flared edges, upstream or downstream, presents an elastic zone bearing on an inclined surface of the adjacent radial wall relative to a radial plane, such that the liner tends to move axially towards the radial wall facing, under action of centrifugal forces, to improve sealing in the zone, and so that when the wheel stops, the elastic zone moves radially inwards, the liner pivoting around an axis distant from the elastic zone.

The invention relates to controlling the leakage zones under theplatforms of the blades of a blade-wheel in a turbomachine.

More precisely, the invention relates to a turbomachine blade-wheelcomprising a disk presenting a plurality of substantially axial slots onits periphery, a plurality of blades having roots that are retained insaid slots, and which blades present platforms for defining the streamof gas on the radially inner side, and upstream and downstream radialwalls which extend from said platforms towards the periphery of saiddisk, inter-blade cavities defined by said platforms and the peripheryof said disk, and sealing devices for sealing the inter-blade spaces,the sealing devices being made in the form of liners having edges thatflare radially inwards and that are disposed in said cavities againstthe walls of the platforms of two adjacent blades.

FIG. 1 is a perspective view showing a sealing liner 1 of the prior artwhich presents an upstream edge 2 and a downstream edge 3 that flareradially inwards, and also two curved longitudinal flaring edges whichfit closely against the flanks of the blades under the platforms. Theupstream and downstream edges 2 and 3 are designed to come into theimmediate vicinity of the adjacent upstream and downstream radial wallsof two adjacent blades, in order to limit leakage through the spaceseparating the adjacent lateral walls. The top wall 6 of each linerbears against the bottom faces of two adjacent platforms under theaction of centrifugal forces when the wheel is rotating and seals thegap between the adjacent platforms. By construction, it is practicallyimpossible for the flared edges to be deformed under the action ofcentrifugal forces, and it is impossible to ensure that the upstream anddownstream flared edges (2 and 3) are pressed effectively against theupstream and downstream radial walls of the blades. As shown in FIG. 2,those edges may be spaced apart from the adjacent radial walls, whichresults in an air leak f between the cavity under the platform and thestream of gas in these zones, which is prejudicial to the efficiency ofthe wheel.

The object of the invention is to have better control over the leakagezone under a blade platform, particularly in the gaps between theunder-platform radial walls.

The invention achieves this object by the fact that each liner presentsan elastic zone on one of its upstream and downstream flared edges, andthe radial walls adjacent to said edges are connected to the platformsby inside surfaces that are inclined relative to a radial plane, andagainst which edges said elastic zone bears, in such a manner that saidelastic zone can slide radially inwards in the event of said wheelceasing to rotate, and radially outwards under the action of centrifugalforces in order to urge said liner to move axially towards the radialwalls distant from said elastic zone so as to improve sealing in saidzone.

In the event of the blade-wheel ceasing to turn, the elastic zone slidesradially inwards and the liner relaxes, moving itself away from thebottom walls of the two platforms, at least in the regions adjacent tothe elastic zone. When the blade-wheel starts to rotate, the centrifugalforces press the liner against the bottom walls of the platforms, andthe elastic forces push the corresponding flared edge towards thelateral walls facing the elastic edge, in order to improve sealing inthis location. Since the elastic zones are still bearing against theadjacent lateral walls, sealing in this zone is guaranteed.

Advantageously, the radial walls that are spaced apart from the elasticzones include abutments to limit the axial movement of the liners underthe action of centrifugal forces.

The lateral walls that are adjacent to the elastic zones also includeabutments to limit inward sliding of said elastic zones.

According to an advantageous characteristic of the invention, theelastic zones are circumferentially defined by two notches that are cutin the corresponding flared edges of the liners. This dispositionfacilitates implementation of the invention at no additional cost.

The invention applies particularly to turbine blade-wheels.

In this specific example, the elastic zone is provided on the upstreamedge, and the angle of the surface that is inclined relative to theradial plane is greater than the slope of the platform relative to theaxis of rotation of the turbomachine.

Other characteristics and advantages of the invention appear on readingthe following description, given by way of example and with reference tothe accompanying figures, in which:

FIG. 1 is a view from below and in perspective of a sealing liner of theprior art;

FIG. 2 is a side view in section of a liner edge and of a radial edge ofa blade, of the prior art;

FIG. 3 is a view from above and in perspective of a sealing liner of theinvention;

FIG. 4 is a view from below and in perspective of the sealing liner inFIG. 3;

FIG. 5 is a section on a plane containing the axis of the blade-wheel,showing the disposition of the sealing liner of the invention in theunder-platform cavity, after assembly and in the absence of centrifugalforces; and

FIG. 6 is similar to FIG. 5 and shows the position of the sealing liner,when it is subjected to centrifugal forces as a result of theblade-wheel rotating.

FIGS. 1 and 2 show the prior art which is described above in the presentdocument.

FIGS. 3 and 4 show a sealing liner 10 of the invention which has edgesthat flare radially inwards, that is, an upstream edge 12, a downstreamedge 13, and between the upstream edge 12 and the downstream edge 13 twolongitudinal inwardly curved flaring edges which fit closely to theshape of the flanks of two adjacent blades.

The upstream edge 12 presents two notches 16 and 17 which define betweenthem an elastic zone 18 which, at rest, projects forwards from theupstream edge 2 of the prior art liner 1 shown in FIG. 1. That is, atrest, the elastic zone 18 lies outside the geometrical surface whichwould join together the ends 12 a and 12 b of the upstream edge 12smoothly and continuously, which ends are situated beyond the notches 16and 17, and connected to the longitudinal edges 14 and 15 respectivelyvia convex surfaces.

FIGS. 5 and 6 show a blade-wheel 30 which comprises a disk 31 thatpresents a plurality of substantially axial slots 32 in its periphery,with each of said slots housing the root of a blade 33. Each blade 33presents a platform 34 above its root, which platform defines theradially inner side of the stream of gas F going through the row ofblades, the platform 34 being connected to an upstream radial wall 35and to a downstream radial wall 36 which extend towards the periphery ofthe disk 31. Inter-blade cavities 37 are thus formed in the periphery ofthe disk 31 under the platforms 34. When the row of blades is observedaxially in the direction of the stream of gas F, each blade 33 presentsa platform portion on the right and a platform portion on the left. Thissame applies to the radial walls 35 and 36. Each under-platform cavity37 is thus defined by right and left platform portions of two adjacentblades and by their right and left upstream and downstream lateral wallportions. By construction and because of assembly requirements, a gap orclearance separates the right hand portion from the left hand portion,which gap needs to be sealed by a sealing liner.

As shown in FIGS. 5 and 6, the connection 38 between the upstream radialwall 35 and the platform 34 presents beside the cavity 37, a surface 39which makes an angle α with the radial plane that is perpendicular tothe axis of rotation of the blade-wheel 30. The downstream radial wall36 is connected to the platform 34 by a zone 40 that presents a curvedsurface 41, beside the cavity 37, said surface being complementary tothe flaring of the downstream edge 13 of the liner 10. Moreover, thedownstream radial wall 36 presents a protuberance 42 on its inside face,said protuberance serving as an abutment for the downstream shoulder ofthe liner 10. The upstream radial wall 35 also presents a protuberance43 on its face situated beside the cavity 37.

The liner 10 is mounted in the cavity 37 in such a manner that itsdownstream edge 13 is positioned above the protuberance 42 and itselastic zone 18 is positioned above the protuberance 43. In thisposition, the elastic zone 18 of the liner 10 bears against the inclinedsurface 39.

The angle α of the inclined surface 39 is calculated as a function ofthe slope of the platform 34 relative to the axis of rotation of thewheel and as a function of the friction angle φ of the liner 10 againstthe inside surface of the platform 34, so that, in the absence of anycentrifugal force, i.e. when the blade-wheel 30 is stationary, theelastic zone 18 slides radially inwards over the inclined surface 39.

In this position most of the surface of the top wall 19 of the liner isspaced apart from the bottom face of the platform 34, as can be seen inFIG. 5, the liner 10 tilting about an axis intersecting the plane ofFIG. 5 at the point referenced 44, said axis being situated near thedownstream flared edge 13. The protuberance 43 on the upstream radialwall 35 serves to prevent the elastic zone 18 from sliding too far, andto retain the liner 10 in the top zone of the cavity 37.

FIG. 6 shows the position of the liner 10 while the blade-wheel 30 isrotating. In this position, the liner 10 is subjected to centrifugalforces which tend to press it against the inside face of the platform34. The elastic zone 18 is urged radially outwards and slides againstthe inclined wall 39.

The angle α is advantageously greater than the slope of the platform 34.When the elastic zone 18 moves outwards, through the fact that the liner10 tilts about the pivot axis defined by the point referenced 44, theelastic force exerted by the elastic zone 18 increases and tends to movethe liner 10 axially towards the downstream radial wall 36, therebyimproving sealing in the connection zone 40. The axial movement of theliner 10 is limited by the protuberance 42 which serves as an abutment.

When the blade-wheel 30 comes to a stop, the liner 10 will return to theposition shown in FIG. 5, as soon as the centrifugal forces areinsufficient to prevent the elastic zone 18 from sliding over theinclined wall 39.

1. A turbomachine blade-wheel comprising: a disk presenting a pluralityof substantially axial slots on its periphery; a plurality of bladeshaving roots retained in said slots, and which blades present platformsfor defining a radially inner side of a stream of gas and upstream anddownstream radial walls that extend from said platforms towards theperiphery of said disk; inter-blade cavities defined by said platformsand the periphery of said disk; and sealing devices configured to sealthe inter-blade spaces, the sealing devices including liners havingedges that flare radially inwards and that are disposed in said cavitiesagainst the walls of the platforms of two adjacent blades; wherein eachsaid liner presents an elastic zone on one of its upstream anddownstream flared edges, and the radial walls adjacent to said edge areconnected to the platforms by inside surfaces that are inclined relativeto a radial plane, and against which edges said elastic zone bears, suchthat said elastic zone is configured to move radially inwards in anevent of said wheel ceasing to rotate, and said elastic zone isconfigured to move radially outwards under action of centrifugal forcesto urge said liner to move axially towards the radial walls distant fromsaid elastic zone to improve sealing in said elastic zone.
 2. A wheelaccording to claim 1, wherein the radial walls that are spaced apartfrom the elastic zones include abutments to limit axial movement of theliners under the action of centrifugal forces.
 3. A wheel according toclaim 1, wherein the lateral walls that are adjacent to the elasticzones include abutments to limit inward sliding of said elastic zones.4. A wheel according to claim 1, wherein the elastic zones arecircumferentially defined by two notches that are cut in thecorresponding flared edges of the liners.
 5. A wheel according to claim1, wherein the elastic zone is provided on the upstream edge.
 6. A wheelaccording to claim 5, wherein the wheel is a turbine blade-wheel.
 7. Awheel according to claim 6, wherein an angle of the inclined surface isgreater than the slope of the platform relative to an axis of rotationof the turbomachine.
 8. A turbomachine comprising: a blade-wheelincluding, a disk presenting a plurality of substantially axial slots onits periphery; a plurality of blades having roots retained in saidslots, and which blades present platforms for defining a radially innerside of a stream of gas and upstream and downstream radial walls thatextend from said platforms towards the periphery of said disk;inter-blade cavities defined by said platforms and the periphery of saiddisk; and sealing devices configured to seal the inter-blade spaces, thesealing devices including liners having edges that flare radiallyinwards and that are disposed in said cavities against the walls of theplatforms of two adjacent blades; wherein each said liner presents anelastic zone on one of its upstream and downstream flared edges, and theradial walls adjacent to said edge are connected to the platforms byinside surfaces that are inclined relative to a radial plane, andagainst which edges said elastic zone bears, such that said elastic zoneis configured to move radially inwards in an event of said wheel ceasingto rotate, and said elastic zone is configured to move radially outwardsunder action of centrifugal forces to urge said liner to move axiallytowards the radial walls distant from said elastic zone to improvesealing in said elastic zone.
 9. The turbomachine according to claim 8,wherein the radial walls that are spaced apart from the elastic zonesinclude abutments to limit axial movement of the liners under the actionof centrifugal forces.
 10. The turbomachine according to claim 8,wherein the lateral walls that are adjacent to the elastic zones includeabutments to limit inward sliding of said elastic zones.
 11. Theturbomachine according to claim 8, wherein the elastic zones arecircumferentially defined by two notches that are cut in thecorresponding flared edges of the liners.
 12. The turbomachine accordingto claim 8, wherein the elastic zone is provided on the upstream edge.13. The turbomachine according to claim 12, wherein the wheel is aturbine blade-wheel.
 14. The turbomachine according to claim 13, whereinan angle of the inclined surface is greater than the slope of theplatform relative to an axis of rotation of the turbomachine.